The basic principles of electrostatographic printing with dry marking material (hereinafter generally referred to as “xerography,” “xerographic printing,” and/or the like) are well known: a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual toner image can be either fixed directly upon the photosensitive member or transferred from the member to another support, such as a sheet of plain paper, with subsequent affixing of the image thereto in one of various ways, for example, as by heat and pressure. To affix or fuse electroscopic toner material onto a support member by heat and pressure, the temperature of the toner material is typically elevated to a point at which its constituents coalesce and become tacky while and pressure is simultaneously applied, thus causing the toner to flow to some extent into the fibers or pores of the support member or otherwise upon the surface thereof. Thereafter, as the toner material cools, solidification of the toner material occurs and the toner material becomes bonded firmly to the support member.
One approach to heat and pressure fusing of electroscopic toner images onto a support has been to pass the support with the toner images thereon between a pair of opposed roller members, at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the fuser roll thereby heating the toner images within the nip. By controlling the heat transferred to the toner, virtually no transfer or “offsetting” of the toner particles from the copy sheet to the fuser roll is experienced under normal conditions. This is because the heat applied to the surface of the roller is insufficient to raise the temperature of the surface of the roller above the “hot offset” temperature of the toner whereat the toner particles in the image areas of the toner liquefy and cause a “splitting” action in the molten toner resulting in “hot offset.” Splitting occurs when the cohesive forces holding the viscous toner mass together become less than the adhesive forces tending to offset it to a contacting surface such as a fuser roll. Occasionally, however, toner particles may be offset to the fuser roll by an insufficient application of heat to the surface thereof (i.e. “cold” offsetting), by imperfections in the properties of the surface of the roll, or by the toner particles insufficiently adhering to the copy sheet by the electrostatic forces which normally hold them there. In such cases, toner particles may be transferred to the surface of the fuser roll with subsequent transfer to the backup roll during periods of time when no copy paper is in the nip. Moreover, toner particles can be picked up by the fuser and/or backup roll during fusing of duplex copies or simply from the surroundings of the reproducing apparatus.
One arrangement for minimizing some of the problems associated with heat and pressure fusing, particularly offsetting, has been to provide the fuser roll with an outer surface or covering of polytetrafluoroethylene, widely distributed under the trademark TEFLON®, to which a release agent such as silicone oil is applied, the thickness of the TEFLON® material being on the order of several mils and the thickness of the oil being less than 1 micron. Alternatively, a layer of silicone rubber or Viton has been be used. The silicone rubber layer may provide conformability with the paper roughness resulting in more uniform fixing and image gloss. Silicone based (polydimethylsiloxane) oils possessing a relatively low surface energy have been found to be suitable for use in the heated fuser roll environment where TEFLON® material constitutes the outer surface of the fuser roll. In practice, a thin layer of silicone oil has been applied to the surface of the heated roll to form an interface between the roll surface and the toner images carried on the support material, thus presenting a low surface energy layer to the toner as it passes through the fuser nip and thereby preventing toner from offsetting to the fuser roll surface. A fuser roll construction of the type described above is fabricated by applying in any suitable manner a solid layer of adhesive material to a rigid core or substrate such as the solid TEFLON® outer surface or covering of the aforementioned arrangement.
Donor roll release agent management (“RAM”) systems have been used as parts of roll fuser apparatuses for some time. Such a RAM system is disclosed in U.S. Pat. No. 4,214,549 to Moser, issued Jul. 29, 1980 (“Moser”). Moser illustrates a heat and pressure roll fusing apparatus for fixing toner images to copy substrates, the toner comprising a thermoplastic resin. The apparatus includes an internally heated, fuser roll cooperating with a backup or pressure roll to form a nip through which the copy substrates pass with the images contacting the heated roll. The heated fuser roll is characterized by an outer layer or surface that, by way of example, is fabricated from a silicon rubber or Viton material to which a low viscosity polymeric release fluid is applied. Release fluid is contained in a sump from which it is dispensed by means of a metering roll and a donor roll, the former of which contacts the release fluid in the sump and the latter of which contacts the surface of the heated fuser roll. The release fluid oil is picked up onto the metering roll as it is rotated through the release fluid oil, which is then metered to a very thin film on the metering roll by a metering blade. In many similar apparatuses, oil is pumped into a trough or collected in a sump wherein it saturates and covers a swiper wick. The metering roll is then loaded to interfere with the swiper wick. Among other things, the wick prevents air entrapment between the moving metering roll and the stationary oil.
Ensuring consistent applications of clean oil to metering rolls via capillary draws through swiper wicks has been challenging.